Chapter 26: Sound
26.1 Origin of Sound

All sounds are made by the vibrations of material objects.


Common Origins of Sound:

Vibrating Strings: piano, violin, guitar
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Vibrating Reed: Saxophone, clarinet
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Fluttering Column of Air (at the mouthpiece): flute
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Vibrating Vocal Chords: your voice
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The original vibration stimulates the vibration of a larger or more massive material...


    • (Some examples of materials that are often stimulated:
      the sounding board of a stringed instrument, the air column within a reed or a wind instrument, or the air in the throat and mouth of a singer.)
...This vibrating material then sends a disturbance through a surrounding medium (usually air) in the form of Longitudinal Waves.

The frequency of the vibrating source = the frequency of sound waves produced.


Pitch – How we describe our subjective impression about the frequency
High Pitched Sound = Hight Vibration Frequency
Low Pitched Sound = Low Vibration Frequency

Infrasonic – Sound waves with frequencies below 20 hertz
Ultrasonic – Sound waves with frequencies above 20,000 hertz
Young can usually hear pitches with frequencies from 20 to 20,000


26.2 Sound in Air
Comression- The pulse of compressed air

Rarefaction- A disturbance in air (or matter) in which the pressure is lowered. Opposite of compression.

26.3 Media That Transmit Sound



26.4 Speed of Sound



26.5 Loudness




26.6 Forced Vibration

Forced Vibration- The vibration of an object that is made to vibrate by another vibrating object that is nearby. The sounding board in a musical instrument amplifies the sound through forced vibration.

26.7 Natural Frequency

Natural Frequency- A frequency at which an elastic object, once energized, will vibrate. Minimum energy is required to continue vibration at that frequency. Also called resonant frequency.

26.8 Resonance

Resonance- A phenomenon that occurs when the frequency of forced vibrations on an object matches the object's natural frequency, and a dramatic increase in amplitude results.

26.9 Interference

26.10 Beats

Beats – The periodic variation in the loudness of sound.